1. Field of the Technology
The present technology relates to a developing device and an image forming apparatus.
2. Description or the Related Art
Copiers, printers, facsimiles, or the like include an image forming apparatus that forms an image by electrophotography. The electrophotographic image forming apparatus forms an electrostatic latent image on a surface of an image bearing member (photoreceptor) using a charging device and an exposure device, develops the electrostatic latent image by supplying developer using a developing device, transfers the developer image on the photoreceptor to a recording medium such as recording paper using a transfer section, and fixes the developer image onto the recording paper using a fixing device and thereby forms an image.
A toner supplied to the photoreceptor by the developing device is contained in a developer tank provided in the developing device. The developer contained in the developer tank is conveyed to a developing roller provided in the developing device. The developing roller rotates while bearing the developer on a surface thereof, and supplies the developer to the photoreceptor. The developer containing the toner is frictionally charged while being conveyed to the developing roller, and the charged developer is moved from the developing roller to the photoreceptor by electrostatic force between the surface of the photoreceptor and the electrostatic latent image. In this manner, the developing device develops the electrostatic latent image on the surface of the photoreceptor, and forms the developer image.
In recent years, accompanying the increase in speed and miniaturization of the image forming apparatus, a developing device capable of quickly and sufficiently performing the charging of the developer has been demanded. For example, Japanese Unexamined Patent Publication JP-A 2004-272017 discloses a circulation-type developing device including a developer conveying section that has a first conveying path, a second conveying path, a first communication path, and a second communication path which are formed by a partition wall provided inside a developer tank, and that conveys the developer in the first conveying path and the second conveying path in directions opposite to each other. The developer conveying section disclosed in JP-A 2004-272017 has a configuration where, to an auger screw type rotation shaft member having a rotation shaft member and a spiral blade spirally wound around the rotation shaft member, a flat plate-like member (fin) parallel with an axial line of the rotation shaft member is provided.
In the developer conveying section described in JP-A 2004-272017, a developer is conveyed in an axial direction of the rotation shaft member by the spiral blade, and the developer is also moved in a direction circumferentially of the rotation shaft member by the main surface of the fin while being electrically charged by friction. However, the negative aspect of the developer conveying section is that the developer is compressed when sandwiched between the spiral blade and the side surface of the fin, and the developer in a compressed state cannot be frictionally charged to a sufficient degree. If such an insufficiently charged developer is used, the image forming apparatus will fail to produce high-quality images.
Further, since the developer conveying section described in JP-A 2004-272017 conveys the developer by a single continuous spiral blade, when a new toner is supplied to the developer tank, the movement of the new toner is obstructed by the spiral blade. As a result, it is difficult for the new toner to diffuse in the axial direction of the rotation shaft member, and unevenness occurs in the concentration of the toner inside the developer tank, which causes image density unevenness in the image formed using the developing device.